The present invention relates to a blank jumping teleprinting method and apparatus applicable in the reproduction and transmission of written data.
Teleprinters essentially comprise two parts, one being used for analysing the document to be transmitted and the other being used for the regeneration thereof. In modern teleprinters, the components used for analysis or regeneration are of the integrated type. They are constituted by a certain number of elements which can read or write in point by point manner a particular document. The number of points constituting these components varies from 4 to 8 per millimeter, depending on the fineness of reproduction required. For the purpose of analysing and reproducing a standard A4 format in general 1728 points are used in the widthwise direction, corresponding to 8 points/mm. In the heightwise direction, the resolution is given by the forward movement of the document, the latter being analysed and reproduced line by line. For a standard resolution, 3.85 lines are transmitted per minute and this is 7.7 lines/minute for high resolution, corresponding to 2 million points in the first case and 4 million in the second.
The capacity of the modulator/demodulator circuits used for transmission are 1400 or 4800 bits/second or 9600 bits/second for special networks. Thus, 416 seconds or approximately 7 minutes are required for transmitting A4 format on a 4800 bit/second network in the standard mode.
To obtain transmission times of approximately 1 minute, it is necessary to compress the data so as to reduce the number of bits to be transmitted. For this purpose, it is possible to code the information in an appropriate language lending itself to compression and a certain number of codes have been developed for this purpose. Another solution which can be combined with the previous solution consists of jumping or skipping those areas in the document which are blank. Thus, a typed or manuscript message generally has many more blanks than black points, particularly the area between the lines, the spaces reserved for titles, the blanks left at the end of lines, etc. There can even be completely blank lines. In order to reduce the amount of information to be transmitted and consequently increase the speed of reproduction, it is of interest to jump all these blank areas.
Blank jumping teleprinter systems have already been proposed. A system of this type is for example described in French patent application No. EN 77 32802 (publication No. 2,369,760) filed on Oct. 28, 1977 and entitled "facsimile compression method and apparatus." Such systems use a strip of 1728 photodetector elements and a memory with the same number of cells. The document is read line by line, each line being read only once. The 1728 binary signals resulting from reading a line are immediately recorded in the memory. This memory is then read to constitute the signals to be transmitted and is carried out in groups of 32 cells. Before transmitting, the 32 bits contained in one of these groups, it is ensured that it contains at least one non-zero bit. If a particular group consists of all zero bits, it is not transmitted and it is then possible to jump to the following group. A jump signal is then produced to control the restoring means on the basis thereof.
This system has the obvious disadvantage of requiring a very large capacity memory because it is necessary to have the same number of memory cells as points analysed in a line.